Universal on-delay timer

ABSTRACT

An on-delay timer comprised substantially entirely of solid state elements for energizing a load a timed interval after the pilot switch is closed. Upon reopening the switch, the load is immediately deenergized and the timer is automatically reset into readiness for another timing operation. The timer is universal in that it can be operated on a wide range of voltages (20 to 132) of either D.C. or 50/60 Hz A.C., and the value of the load current can be from a few milliamperes to a value limited by the capabilities of the components used, such as one ampere for a typical timer. It incorporates a leaky switch detector that enables proper operation even if the switch leaks current to some extent. An indicator indicates &#39;&#39;&#39;&#39;off,&#39;&#39;&#39;&#39; timing (flashing) and &#39;&#39;&#39;&#39;on &#39;&#39;&#39;&#39; conditions.

United States Patent [191 Schuchmann et all. .lune4, 1974 [54] UNIVERSALQN-DELAY TIMER 3,641,397 2/l972 Elliot et al., 3l7/l4l S [75] Inventors:Russell P. Schuclunann, Racine;

. Herman P. Schutten, Elm Grove; zz f x 'fi g g g E h r W A IsadoreSmall, lll, Milwaukee; A 2 e Donald L. Van Zeeland, Franklin, all u of57] ABSTRACT [73] Asslgnee? Cqtler-Hammer, Mllwaukee An on-delay timercomprised substantially entirely of solid state elements for energizinga load a timed in- [22 Filed; 0m 10 1972 terval after the pilot switchis closed. Upon reopening the switch, the load is immediatelydeenergized and [2]] Appl- 296,275 the timer is automatically reset intoreadiness for an- 1 other timing operation. The timer is universal inthat it 52] us. Cl. ..307' 141,317/141s can be Operated on a wide rangeof voltages to [51 1'- rm. Cl. *1/00 ofeirher D0 or 50/60 Hz and thevalue of [58] Field of Search 317/141 5, 142, 148.5 B; the loadCurrent-can be from a f milliamperes to a 302/141 R; 315/360 valuelimited by the capabilities of the components used, such as one amperefor a typical timer. lt incor -R f Cited porates a leaky switch detectorthat enables proper UNITED STATES PATENTS operation even if the switchleaks current to some ex- 3 512048 5/1970 W H t t 1 317/141 S tent. Anindicator indicates off," timing (flashing) Ll en OWI Z e a u n I3,555,367 1/1971 W atson s n/141 s and on commons 3584262 6/197! Gary317/141 5 10 Claims, 1 Drawing Figure 1.1 Pan 2 meal/r lei/ i l ans/a H5an 2) m/a/mrm @3 3 c/ecu/r I p4 m6 r/M/Na I Ian a6 c/eca/r II 5% gm #154 a ll g 12/4 5 I s .zor I is if} 31' l T mg? L 1 723 m 1a m a we 1;? Q8vvvvv Q I L 43 k5 Le! 65 c I LIMP i) h w- Q :5 l

1 UNIVERSAL ON-DELAY TIMER BACKGROUND OF THE INVENTION SUMMARY OF THEINVENTION This invention relates to solid state on-delay timers.

An object of the invention is to provide an on delay timer of theuniversal type, meaning that it has a wide range of application'todifferent voltages and loads.

A more specific object of the invention is to provide an on-delay timerthat will operate properly on a wide range of supply voltage values.

Another specific object of the invention is to provide an on-delay timerthat will operate properly on either DC. or AC. power.

Another specific object of the invention is to provide an on-delay timerthat will supply a wide range of load currents.

Another specific object of the invention is to provide an on-delay timerthat will control either resistive or inductive loads.

Another specific object of the invention is to provide an on-delay timerwith leaky switch detection means enabling proper operation if, onclosing, the pilot switch impedance goes below a predetermined level andif, on opening, the pilot switch impedance goes above apredeterminedhigher level.

Another specific object of the invention is to provide an on-delay timerwith an indicator that is off when the load is deenergized, flashes whenthe timer is timing, and is on when the load is energized.

Another specific object of the invention is to provide an on-delay timerthat resets if the pilot switch is reopened during the timing interval.

Another specific object of the invention is to provide an on-delay timerhaving combinations of the aforementioned features.

Other objects and advantages of the invention will hereinafter appear.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE of the drawing showsa semiconductor universal on-delay timer constructed in accordance withthe invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, thereis shown a solid state universal on-delay timer system according to theinvention. This timer system'is a delay on energization or ondelay timerin that it energizes a load' L a predetermined time interval afterclosure of pilot switch SW.

This timer system is supplied with electrical power through a pair ofpower line terminals LI and L2 shown at the left side of the drawing.This electrical supply may be either AC. or DC. and may have a widerange of voltage between 20 and 132 volts.

The load circuit comprises a path from terminal LI through pilot switchSW, triac Q3 and load L to terminal L2. As will be apparent, when pilotswitch SW is closed and triac O3 is fired into conduction, the load willbe energized with AC. or DC. depending upon which type of supply isconnected to the line terminals.

The system is provided with a power supply circuit for supplying controlvoltage of 15 volts DC. to the timer circuit. This power'supply circuitcomprises primarily transistors 01 and Q4. As shown at the left part ofthe drawing, the base of transistor OI is supplied with voltage from avoltage divider comprising a rectifying diode Dland resistors Rll, R2and R3 connected in series in that order from terminal L1 to terminalL2. The base of transistor O1 is connected to the junction betweenresistors R1 and R2. The emitter of transistor O1 is supplied withvoltage from terminal Ll through switch SW and rectifying diode D2 whilethe collector thereof is connected through resistors R4 and R5 in seriesto terminal L2. From this it will be apparent that whenever switch SW isclosed, transistor Q] will be rendered conducting as long as theimpedance of the closed switch is below a predetermined low value,hereinafter described in connection with the leaky switch detectioncircuit. Also, whenever switch SW is opened, transistor Q1 will berendered nonconducting as long as the impedance of the open switch isabove a predetermined high value as hereinafter described.

Also in this power circuit for supplying transistor O4 with voltage, arectifying circuit extends from terminals Ll through switch SW, arectifying diode D3 and current limiting resistor R1] in series to thecollector of transistor Q4. The base of transistor O4 receives voltagethrough resistor R7 from the collector of transistor Q1. The emitter oftransistor O4 is connected through a reverse-blockingdiode D4 toconductor 2 to supply 1; volts. DC. or the like thereto.

Transistor O4 is a power transistor connected as an emitter follower tosupply the control voltage to the timer and indicator circuits to theright thereof.

Also in this power circuit, a zener diode ZDI is connected from the baseof transistor 04 to terminal L2. This may be a 15 volt z'ener diode orthe like to regulate the DC. voltage on conductor 2 at l5 volts.

The aforementioned leaky switch detector circuit is incorporated intothis power circuit. This leaky switch detection is accomplished withtransistor Q1, its base bias circuit including resistors R1, R2 and R3and resistor R6. This latter resistor R6 is in series in the circuitextending from terminal Ll through switch SW, diode D3 and resistor R6to terminal L2. Resistor R6 forms with the impedance of switch SW avoltage divider whose junction is connected through diode D2 to theemitter of transistor 01. Thus, the switch impedances at whichtransistor Q1 will turn on and off can be pre determined by the basebias voltage and the value of resistor R6.

A filter circuit comprising a capacitor C4 and a resis- A resetdisabling switching transistor O2 is provided to shunt the inputs toreset transistors Q5 and O6 whenever the pilot switch is closed and thesystem is operating. At other times, the reset transistors conduct todischarge the filter capacitor and timing capacitor, respectively. Forthis purpose, the collector of transistor 02 is supplied with voltagefrom the junction between resistors R2 and R3. The base of transistor O2is supplied with voltage from the junction between resistor R4 and itsbase bias resistor R5 and its emitter is connected to terminal L2.

Filter reset transistor O5 receives base current through its base biasresistor R12 from. the junction of resistors R2 and R3, and receivescollector current through current limiting resistor R14 from DC.conductor litsemitter being connected to terminalls2 A transient voltagesuppressing capacitor C 1 is connected from the junction of resistors R2and R3 to terminal L2 to prevent inadvertent turn-on of the resettransistors.

Timer reset transistor Q6 receives base current from the junction ofresistors R2 and R3 through its base bias resistor R13 and receivescollector voltage from the timer circuit as hereinafter described itsemitter is connected to terminal L2.

The timer circuit is provided with a regulated volt D.C. supply. Forthis purpose current limiting resistor R16 and a 10 volt zener diode ZD2are connected in series from DC. conductor 2 to terminal L2. Thejunction of resistor R16 and zener diode ZD2 is connected to 10 voltD.C. conductor 4.

The timer circuit comprises a bridge circuit supplied with voltageacross conductor 4 and terminal L2 and provides the control bias voltagefor a programmable unijunction-transistor (PUT) Q7 used as a triggerdevice. For this purpose, the left leg of the bridge comprises avariable resistor P], a fixed resistor R17 and a timing capacitor C5connected in that order from conductor 4 to terminal L2. The junctionbetween resistor R17 and capacitor C5 is connected through currentlimiting resistor R18 to the anode of PUT Q7. The right leg of thebridge comprises resistors R19 and R20 connected in series fromconductor 4 to terminal L2. The junction between resistors R19 and R20is connected to the gateof the PUT. A capacitor C6 is connected acrossresistor R20 to delay the drop of voltage on the gate of the PUT andprevent its falling below its anode I voltage and thereby to preventfiring of the PUT when the timer is being reset.

The collector-emitter circuit of the aforementioned timer resettransistor 06 is connected across resistor R18 and capacitor C5 todischarge this timer capacitor.

The output of the timer circuit is used to fire an SCR that energizes areed relay that, in turn, renders the aforementioned triac Q3 conductivein the load circuit. For this purpose, the cathode of the PUT isconnected to the gate of silicon controller rectifier (SC R) Q8. Theanode of the. SCR is supplied with voltage from conductor 2 throughlight emitting diode LED and the coil CR of an isolating reed relay. Thecathode of the SCR is connected to terminal L2. A transient voltagesuppressingcapacitor C7 is connected between the gate and cathode of theSCR. A gate bias register R21 is connected between the gate and cathodeof the SCR. A transient voltage suppressing capacitor C8 is alsoconnected across the SCR Q8 anode-cathode terminals.

The flasher indicator circuit comprises a light emitting diode LED and astate indicator circuit that causes it to be off when the load is notenergized, to flash when the system is timing, and to provide a steadylight when the load isenergized.

This state indicator circuit comprises a voltage divider includingresistors R22 and R23 in series connected from DC. conductor 2 toterminal L2. The junction between resistors R22 and R23 is connected tothe base of transistor Q10 to apply a base current thereto. A flashercontrol capacitor C9 and a resistor R24 are connected in series fromconductor 2 to terminal L2. The junction between capacitor C9 andresistor R24 is connected to the emitter of transistor 010.

In this state indicator circuit, the emitter of transistor O9 issupplied with voltage fromconductor 2 through resistor R25 while thecollector thereof is connected to the base of transistor O10. Thejunction of light emitting diode LED and reed relay coil CR is connectedthrough resistor R26 to the base of transistor 09, and the emitter oftransistor 09 is connected through resistor R27 to the junction betweenreed relay coil CR and the anode of the SCR. Resistor R27 is much largerin resistance value than coil CR and resistor R26 together so that theresistance of the base-emitter path through resistor R27, coil CR andresistor R26 is primarily determined by resistor R27 for reasonshereinafter described.

OPERATION OF THE STATE INDICATOR Assuming that SCR O8 and transistors 09and Q10 are initially non-conducting, the voltage divider applies a biascurrent to the base of transistor Q10. Initially a higher positivevoltage is applied to the emitter from conductor 2 through capacitor C9to reverse bias the base-emitter circuit and hold transistor O10nonconducting.

As capacitor C9 charges by current flow through resistor R24, thevoltage at the emitter of transistor Q10 decreases below the voltage onthe base to start the transistor conducting at about 0.6 volt forwardbaseemitter voltage. At low values of collector current, the collectorcurrent of transistor Q10 is shunted around the emitter-base circuit oftransistor 09, that is, it flows through the shunt path formed byresistor R27, coil CR and resistor R26. Since resistor R27 is muchlarger in resistance value than coil CR and resistor R26 such as 220kilohms as against 470 ohms for resistor R26, the resistance of'theshunt path is determined primarily by resistor R27. Resistor R27 servestwo purposes. It shunts Q8 and Q10 leakage currents around theemitter-base circuit 'of transistor 09 and thereby prevents spuriousturn-on of the 09-010 pair due to leakage current. It also establishesthe peak point current of the the 09-010 pair in that the currentflowing in transistor O10 must reach a value to develop 0.6 volt acrossresistor R27 before transistor Q9 conducts and regeneration in the09-010 pair occurs.

When capacitor C9 charges to the point where the base-emitter junctionof transistor Q10 becomes sufficiently forward biased, the 09-010transistor pair switches on. That is, the voltage drop across resistorR27 causes emitter-base current to flow-in transistor Q9 to render itconducting. The transistor O9collector current then goes to thebase-emitter junction oftransistor Q10 to turn the latter on more,causing transistor ()9 to conduct more, etc., causing regeneration.

This regenerating conduction of the transistor pair allows capacitor C9to discharge. This discharge current flowsprimarily through lightemitting diode LED, resistor R26 and transistor Q10 to light the LED,but some current also flows through the secondary path consisting ofresistor R25, emitter-collector of transistor O9 and base-emitter of thetransistor 010. The initial discharge current is limited by resistor R26which also serves to lengthen the discharge time thereby to provide amore visible LED flash. Since the initial discharge current has a highvalue, the LED brightness is high. Since the pulse current through theLED is obtained from charge stored on capacitor C9, both the steadystate and pulse current demands from the voltage supply from conductor 2are low.

The indicator LED is now lit and will be extinguished when capacitor C9has discharged. For this purpose, as the discharge current fromcapacitor C9 decays to zero, the voltage drop across resistor R26becomes snall so that the voltage at the base of transistor 09 isprovided primarily by the diode voltage drop characteristic of the LED.The voltage drop across the LED is substantially constant at about 1.5volts over a wide range of currents. Thus, the voltage across resistor Ris maintained at this voltage minus the emitter-base junction drop oftransistor 09 or 1.5 minus 0.6 which is 0.9 volts; Under theseconditions, the circuit including the LED, transistor Q9 and theresistor R25 is equivalent to a current source that injects a current of0.41 matvoltage 0.9 divided by 2,200 ohms resistance of resistor R25into the junction between the base of the transistor Q10 and resistorsR22 and R23. The current provided by this current source determines theturn-off point of the (39-010 pair. As capacitor C9 discharges, thevoltage at the emitter oftransistor 010 will rise until it reaches agiven value at which the curent being drawn through the voltage divideris equal to the current provided by this current source. Thus, no basedrive current is available for transistor Q10 and transistors Q10 and Q9are rendered non-conducting, causing the indicator LED to beextinguished.

Capacitor C9 is then free to resume charging to provide a second flashin a similar manner. The flash rate is preferably about two per second.

When SCR O8is fired into conduction as hereinafter described, currentwill flow continuously from conductor 2 through the LED, coil CR and theSCR to provide a steady indication.

OPERATION OF THE TlMl NG SYSTEM When this system is used on a DC.supply, the positive side is connected to terminal L1 and the negativeor grounded side is connected to terminal L2. This causes current flowthrough diode D1 and resistors R1, R2 and R3 to apply a bias voltage onthe base of transistor Q1 that is lower than the supply voltage inaccordance with the drop in diode D1 and resistor R1.

For on-delay energization of load L, switch SW is closed. Current flowsfrom terminal L1 therethrough 6 and through diode D3 and resistor R6 toterminal L2.

The leaky switch detection occurs as follows. The impedance of theclosed switch SW and resistor R6 form a voltage divider. The voltagefrom the junction of this divider is applied through diode D2 to theemitter of transistor Q1. it will be apparent that the higher theimpedance of the closed switch, the lower this emitter voltage will be.This transistor will not be rendered conducting unless its emitter-basejunction is forward biased. Thus, the transistor detects the impedanceof the pilot switch and will allow proper operation if the closed switchimpedance is low enough such as less than ohms, for example. Onreopening, the load will deenergize if the open switch impedance is highenough such as greater than 40,000 ohms, for example, as hereinafterdescribed.

On closure of switch SW, assuming its impedance is less than 100 ohms,transistor 01 is turned on, causing current flow through diode D2,emitter-collector junction of transistor Q1 and resistors R4 and R5. Thevoltage drop across resistor R5 forward biases the baseemitter junctionof transistor O2 to render the latter conducting thereby to shunt basecurrent from resettransistors Q5 and 06. This keeps the resettransistors Q5 and Q6 turned off, allowing the filter capacitor C4 andtiming capacitor C5 to charge as hereinafter described.

.Closure of switch SW as aforesaid also applies the supply voltageacross triac Q3 and load L. The supply voltage is also applied by switchSW through diode D3 and resistor R11 to the collector of powertransistor Q4. Current from the collector of transistor 01 is appliedthrough resistor R7 to the base of transistor 04 to render the latterconducting. This causes a DC. voltageto be applied through transistor 04and diode D4 to conductor 2. Zener diode ZDl at the base of transistorQ4 regulates this voltage to l5 volts DC.

The filter comprising capacitor C4 and resistor R15 smooths the DC.voltage when the system is used with an AC. power supply.

The timer circuit supply voltage is taken from the DC. conductor.Current flows from conductor 2 through resistor R16 and Zener diode ZDZto regulate the voltage on conductor 4 at 10 volts D.C.

For the timing function, current flows through variable resistor P1 andresistor R117 to charge timing capacitor C5, the charging rate and thusthe time interval being set at variable resistor P1. Current also flowsthrough resistors R19 and R20 in the other leg of the bridge to apply abias voltage from the junction of this voltage divider to the gate ofPUT Q7. Capacitor C6 charges to the voltage across resistor R20. Now,when timing capacitor C5 charges, the voltage on the anode of the PUTincreases. This charging time is the time interval of the on-delaysystem. During this time interval, since the DC. control voltage isbeing applied to the flasher indicator circuit, the LED flashes in themanner hereinbefore described to indicate that the system is timing.Before switch SW was closed, of course, the LED was off since there wasno voltage on conductor 2.

The timing interval terminates when the anode voltage of the PUT exceedsthe level of the gate voltage. At this time, the PUT triggers on andapplies current from its cathode to the gate of SCR Q8 to fire thelatter into conduction. As a result, current now flows through the LED,coil CR and the SCR to energize the reed relay and close its contactCR1. As a result, current flows into the gate of triac O3 to fire thetriac into conduction thereby toenergize the load.

The current flow in the SCR maintains the LED continuously lighted toindicate that the load is energized.

When switch SW is reopened, the load is deenergizes instantly andwithout any time delay if the impedance across the open switch is 40,000ohms or'more. If the switch impedance is at least that amount, thevoltage drop across it will be enough to reverse bias the emitter-basejunction of transistor 01 to render it nonconducting. This switch thusopens the load circuit to deenergize the load. The switch alsodisconnects the control voltage so that the reed relay is deenergizedand its contact opened and the LED is extinguished to indicate that theload is deenergized.

The circuit is reset as follows. Opening of switch SW removes the basecurrent from transistor Q2, rendering the latter nonconducting so it nolonger shunts the base-emitter junctionsof the reset transistors.Conse-' quently, the voltage across resistor R3 is now applied to biasthe base-emitter junctions of transistors Q5 and 06 on. As a result,filter capacitor C4 discharges through resistor R14 and thecollectingemitter junction of transistor O5. And timing capacitor C5discharges through resistor R18 and the collector-emitter junction oftransistor O6. in this manner, the capacitors are reset to zero chargeso that the system will always start from the same point when switch SWis closed resulting inaccurate timing repeatability.

When A.C. power is connected to terminals L1 and L2, the system operatesin substantially the same manner as with DC. power except that half-waverectified power is used for control purposes and full-wave power is usedfor the load. Thus, the positive half-cycle of the supply voltage isapplied through diodes D1, D2 and D3 and the negative half-cycle isblocked. Also, the positive half-cycle of voltage is applied throughpower transistor Q4 and diode D4 to the DC. conductor and the negativehalf-cycle is blocked. Under this condition, the rectified half-wavevoltage on the DC. conductor is smoothed by filter C4-Rl5 to providesmooth unidirectional voltage for operation of the timer circuit and theflasher indicator circuit in the manner hereinbefore described. Whencontact CR1 is closed at the end of the timedelay period, triac O3 isfired on each half-cycle to provide full-wave A.C. energization of theload. For'this purpose, the gating pulse of current must be applied tothe gate of the triac to render it conducting. When terminal L1 ispositive, current flows through contact CR1 and resistor R8 into thegate and out of the lower terminal of triac O3 to render it conducting.When terminal L2 is positive on alternate halfcycles of the supply A.C.voltage. current flows into the lower terminal and out of the gate andthen through resistor R8 and contact CR1 to fire the triac intoconduction.

Reed relay CR electrically isolates the control circuit from the poweroutput (load) circuit.

While the system hereinbefore described is effectively adapted tofulfill the objects stated, it is to be understood that the invention isnot intended to be confined to the particular preferred embodiment ofuniversal on-delay timer disclosed inasmuch as it is susceptible ofvarious modifications without departing from the scope of the appendedclaims.

We claim:

1. A universal on-delay timer system that operates properly on any powersupply voltage through a wide range of voltages of either AC or DC. toenergize a load a time interval after closure of a pilot switchcomprising:

' an electrical power supply source;

a load circuit including power switching means controllable to connectsaid source to said load;

a control circuit comprising a timer circuit including triggering meansoperable by said timer circuit at the end of a precisely measured timeinterval;

a power conversion circuit fed from said source for providing a controlvoltage of predetermined value for a wide range of power supply voltagesof either AC. or DC;

a pilot switch operable to control energization and deenergization ofthe load;

means including said power conversion circuit responsive to closure ofsaid pilot switch for applying said control voltage to operate saidtimer circuit;

means including control switching means responsive to said triggeringmeans at time-out of said timer circuit for operating said powerswitching means to energize the load at the end of a precisely measuredtime interval for accurate repeatability;

said control switching means including means electrically isolating saidcontrol circuit from said load circuit,

2. The invention defined in claim 1, wherein said pilot switch iseffective upon reopening thereof for controlling immediatedeenergization of the load.

3. A universal on-delay timer system that operates properly on any powersupply voltage through a wide range ofvoltages of either AC. or DC. toenergize a load a time interval after closure of a pilot switchcomprising:

an electrical power supply source;

a load circuit including power switching means controllable to connectsaid source to said load;

a control circuit comprising a timer circuit;

a power conversion circuit fed from said source for providing a controlvoltage of predetermined value for a wide range of power supply voltagesof either a pilot switch operable to control energization anddeenergization of the load;

means including said power conversion circuit responsive to closure ofsaid pilot switch for applying said control voltage to operate saidtimer circuit;

' means including control switching means responsive to time-out of saidtimer circuit for operating said power switching means to energize theload;

said control switching means including means electrically isolating saidcontrol circuit from said load v circuit;

said pilot switch being effective upon reopening thereof for controllingimmediate deenergization of the load;

said power conversion circuit incorporating:

a leaky switch detection circuit comprising:

impedance means;

and means for detecting the relative impedance of said pilot switch andto allow proper operation under conditions where the closed pilot switchimimately 100 ohms and said predetermined large value is approximately40,000 ohms.

5. A universal on-delay timer system that operates properly on any powersupply voltage through a wide range of voltages of either A.C. or DC. toenergize a load a time interval after closure of a pilot switchcomprising:

an electrical power supply source;

a load circuit including power switching meanscontrollable to connectsaid source to said load;

a control circuit comprising a timer circuit;

a power conversion circuit fed from said source for providing a controlvoltage of predetermined value for a wide range of power supply voltagesof either A.C. or DC;

a pilot switch operable to control energization and deenergization ofthe load;

means including said power conversion circuit responsive to closure ofsaid pilot switch for applying said control voltage to operate saidtimer circuit;

means including control switching means responsive to timeout of saidtimer circuit for operating said power switching means to energize theload;

said control switching means including means electrically isolating saidcontrol circuit from said load circuit;

said control circuit comprising:

an indicator circuit fed from said control voltage comprising:

a visual indicator that is off when said pilot switch is open;

means responsive to closure of said pilot switch to initiate timing forcausing said visual indicator to operate in a flashing mode;

and means responsive to said control switching means at time-out forterminating said flashing mode and operating said visual indicator in acontinuous indication mode.

6. The invention defined in claim 1, wherein said control circuitcomprises:

semiconductor means for resetting said timer circuit so that each timingcycle is uniform for accurate repeatability;

and reset disabling means responsive to closure of said pilot switch forrendering said resetting means ineffective. and being responsive toreopening of said pilot switch for allowing operation of said resettingmeans.

7. A universal on-delay timer system that operates properly on any powersupply voltage through a wide range of voltages of either A.C. or DC. toenergize a load a time interval after closure of a pilot switchcomprising:

an electrical power supply source; e

a load circuit comprising a triac and a pilot switch operable to connectsaid load circuit to said power supply source and to initiate operationof the system;

a control circuit comprising a timer circuit and an indicator circuit;

a power conversion circuit fed from said source for providing aregulated unidirectional control volt age of predetermined value for awide range of power supply voltages above said value and of ei-. therA.C. or DC;

means including said power conversion circuit responsive to to operationof said pilot switch for providing said unidirectional control voltageto said control circuit to initiate operation of said timer circuit;

a visual indicator and means in said indicator circuit responsive tosaid unidirectional control voltage while said timer is timing forcausing flashing of said visual indicator;

and control switching means responsive to time-out of said timer circuitfor firing said triac into conduction to energize said load and forcontinuously energizing said visual indicator. g

8. The invention defined in claim 7, wherein said power conversioncircuit incorporates:

a leaky switch detector circuit comprising:

a detector transistor;

means fed from said power supply source for applying a bias voltage tosaid transistor;

means comprising an impedance forming with said pilot switch a voltagedivider fed from said power supply source to apply an operating voltageto said transistor in opposition to said bias voltage;

and said bias voltage and said impedance being proportional so that saidtransistor conducts when the closed pilot switch impedance is below apredetermined small value and stops conducting when the.

open pilot switch impedance is above a predetermined large value. 9. Theinvention defined in claim 8, wherein said power conversion circuit alsocomprises:

means comprising an emitter-follower power transistor. fed from saidpower supply source and being responsive to conduction of said detectortransistor for providing said unidirectional control voltage. 10. Theinvention defined in claim 7, wherein said control switching meanscomprises:

a reed relay for firing said triac into conduction; and a semi-conductorcontrolled rectifier for energizing said reed relay and for continuouslyenergizing said visual indicator.

1. A universal on-delay timer system that operates properly on any powersupply voltage through a wide range of voltages of either A.C. or D.C.to energize a load a time interval after closure of a pilot switchcomprising: an electrical power supply source; a load circuit includingpower switching means controllable to connect said source to said load;a control circuit comprising a timer circuit including triggering meansoperable by said timer circuit at the end of a precisely measured timeinterval; a power conversion circuit fed from said source for providinga control voltage of predetermined value for a wide range of powersupply voltages of either A.C. or D.C.; a pilot switch operable tocontrol energization and deenergization of the load; means includingsaid power conversion circuit responsive to closure of said pilot switchfor applying said control voltage to operate said timer circuit; meansincluding control switching means responsive to said triggering means attime-out of said timer circuit for operating said power switching meansto energize the load at the end of a precisely measured time intervalfor accurate repeatability; said control switching means including meanselectrically isolating said control circuit from said load circuit. 2.The invention defined in claim 1, wherein said pilot switch is effectiveupon reopening thereof for controlling immediate deenergization of theload.
 3. A universal on-delay timer system that operates properly on anypower supply voltage through a wide range of voltages of either A.C. orD.C. to energize a load a time interval after closure of a pilot switchcomprising: an electrical power supply source; a load circuit includingpower switching means controllable to connect said source to said load;a control circuit comprising a timer circuit; a power conversion circuitfed from said source for providing a control voltage of predeterminedvalue for a wide range of power supply voltages of either A.C. or D.C.;a pilot switch operable to control energization and deenergization ofthe load; means including said power conversion circuit responsive toclosure of said pilot switch for applying said control voltage tooperate said timer circuit; means including control switching meansresponsive to time-out of said timer circuit for operating said powerswitching means to energize the load; said control switching meansincluding means electrically isolating said control circuit from saidload circuit; said pilot switch being effective upon reopening thereoffor controlling immediate deenergization of the load; said powerconversion circuit incorporating: a leaky switch detection circuitcomprising: impedance means; and means for detecting the relativeimpedance of said pilot switch and to allow proper operation underconditions where the closed pilot switch impedance is a predeterminedsmall value or less and where the open pilot switch impedance is apredetermined large value or more, and where the applied voltage mayvary over a wide range.
 4. The invention defined in claim 3, wherein:said predetermined small impedance value is approximately 100 ohms andsaid predetermined large value is approximately 40,000 ohms.
 5. Auniversal on-delay timer system that operates properly on any powersupply voltage through a wide range of voltages of either A.C. or D.C.to energize a load a time interval after closure of a pilot switchcomprising: an electrical power supply source; a load circuit includingpower switching means controllable to connect said source to said load;a control circuit comprising a timer circuit; a power conversion circuitfed from said source for providing a control voltage of predeterminedvalue for a wide range of power supply voltages of either A.C. or D.C.;a pilot switch operable to control energization and deenergization ofthe load; means including said power conversion circuit responsive toclosure of said pilot switch for applying said control voltage tooperate said timer circuit; means including control switching meansresponsive to timeout of said timer circuit for operating said powerswitching means to energize the load; said control switching meansincluding means electrically isolating said control circuit from saidload circuit; said control circuit comprising: an indicator circuit fedfrom said control voltage comprising: a visual indicator that is offwhen said pilot switch is open; means responsive to closure of saidpilot switch to initiate timing for causing said visual indicator tooperate in a flashing mode; and means responsive to said controlswitching means at time-out for terminating said flashing mode andoperating said visual indicator in a continuous indication mode.
 6. Theinvention defined in claim 1, wherein said control circuit comprises:semiconductor means for resetting said timer circuit so that each timingcycle is uniform for accurate repeatability; and reset disabling meansresponsive to closure of said pilot switch for rendering said resettingmeans ineffective, and being responsive to reopening of said pilotswitch for allowing operation of said resetting means.
 7. A universalon-delay timer system that operates properly on any power supply voltagethrough a wide range of voltages of either A.C. or D.C. to energize aload a time interval after closure of a pilot switch comprising: anelectrical power supply source; a load circuit comprising a triac and apilot switch operable to connect said load circuit to said power supplysource and to initiate operation of the system; a control circuitcomprising a timer circuit and an indicator circuit; a power conversioncircuit fed from said source for providing a regulated unidirectionalcontrol voltage of predetermined value for a wide range of power supplyvoltages above said value and of either A.C. or D.C.; means includingsaid power conversion circuit responsive to to operation of said pilotswitch for providing said unidirectional control voltage to said controlcircuit to initiate operation of sAid timer circuit; a visual indicatorand means in said indicator circuit responsive to said unidirectionalcontrol voltage while said timer is timing for causing flashing of saidvisual indicator; and control switching means responsive to time-out ofsaid timer circuit for firing said triac into conduction to energizesaid load and for continuously energizing said visual indicator.
 8. Theinvention defined in claim 7, wherein said power conversion circuitincorporates: a leaky switch detector circuit comprising: a detectortransistor; means fed from said power supply source for applying a biasvoltage to said transistor; means comprising an impedance forming withsaid pilot switch a voltage divider fed from said power supply source toapply an operating voltage to said transistor in opposition to said biasvoltage; and said bias voltage and said impedance being proportional sothat said transistor conducts when the closed pilot switch impedance isbelow a predetermined small value and stops conducting when the openpilot switch impedance is above a predetermined large value.
 9. Theinvention defined in claim 8, wherein said power conversion circuit alsocomprises: means comprising an emitter-follower power transistor fedfrom said power supply source and being responsive to conduction of saiddetector transistor for providing said unidirectional control voltage.10. The invention defined in claim 7, wherein said control switchingmeans comprises: a reed relay for firing said triac into conduction; anda semi-conductor controlled rectifier for energizing said reed relay andfor continuously energizing said visual indicator.